The example embodiments relate to a physical unclonable function systems and methods. A physical unclonable function (PUF) produces a unique number associated with an electronic component, such as an integrated circuit. Moreover, the uniqueness of the number derives from the likewise unique physical attributes of the generating circuit. Such unique physical attributes arise from any variation as between one device and the next of the same design, due to the inherent difference in each such device—for example, process variations, and unintended yet unavoidable physical electrical variances, can slightly alter the response of plural devices, all having the same intended design. The PUF circuitry possessing such variations can, in a given instantiation, be energized and a resultant data signal can be read. As a result of the device variations, the respective read data value will differ from device to device, despite the common design among those devices. In this sense, the number may be considered a digital “signature,” “fingerprint,” “key,” or the like, of the device, all connoting each same-design device's unique data value.
The goal for a successful PUF is that for a given device, the unique (or random) value it produces is repeatable each time it is energized, so as to provide the signature of that device. Moreover, as the term “unclonable” suggests, also preferred of such devices is that the precise digital signature of one device cannot be readily cloned by another, so as to keep secure the unique value of each different PUF device, that is, to render the value of one device unpredictable from another device of the same design. Various approaches are known in the art to constructing PUFs, and heretofore such approaches have yielded repeatable randomness of about 85%, that is, for a given, repeatable, random number output from a PUF device, at least 85% of the bits of the number remain unchanged from one instantiation of the random number generation to the next. However, such an approach leaves 15% of the bits that will still change from one instantiation to the next, and there often is little or no predictability as to which bits in the total digital signature will be those that form the 15% change. Hence, the art endeavors to achieve greater repeatability or, stated alternatively, less change in the total digital signature from different instantiations thereof.
Given the preceding, the present application provides alternatives to and improvements to prior art PUF devices, as further detailed below.